Field of Invention
The present invention relates to an openwork load-bearing structure, in particular a lattice tower structure for a wind turbine. In particular, the invention relates to a foundation structure, which is embodied as an openwork load-bearing structure, in particular as a lattice tower structure, and which is anchored to the ground, for example, as an offshore foundation structure by means of driven foundation piles, in particular by means pre-driven hollow piles. Furthermore, the present invention relates to a method for producing an openwork load-bearing structure, in particular a lattice tower structure.
Brief Description of Related Art
Openwork load-bearing structures include, for example, tripods, tripiles or lattice tower structures. The invention will be discussed using such lattice tower structures as an example, without this being intended to be limiting. Lattice tower structures in the context of wind turbines are well known, for example, as lattice towers for wind turbines as an alternative to tubular steel towers. Also known are tower lattice structures as foundation structures, via which a structure is connected to the ground. Such known foundation structures, for example, consist of a lattice structure of corner posts and framework-like struts that are arranged between the corner posts. In other openwork load-bearing structures the term used is legs rather than corner posts. The anchoring to the ground, e.g. to the seabed, is carried out, for example, via driven foundation piles, for example embodied as hollow piles in order to be able to receive the lower ends of the corner posts. Then, grout is filled into the hollow piles to firmly connect the corner posts to the piles. In general, the corner post is extended at its free end using so-called jacket legs for the connection to the foundation piles. These jacket legs are positioned in such a way that in the vertical direction they stand in the foundation piles, while the corner posts are tilted with respect to the vertical direction. According to the terminology of the present application these jacket legs are part of the corner post and thus included in the term “corner post”. Thus, connecting the corner posts with the piles can therefore also be connecting the jacket legs with the piles.
Generally, these known foundation structures are referred to as jacket foundations and are mainly used in the offshore area, that is the foundation structure is in the sea, and the hollow piles are anchored to the seabed. On the foundation structure, there may be arranged a tower structure, especially a wind turbine, for example, a wind turbine with a lattice or a tubular steel tower.
The aforementioned lattice tower structures consist of so-called primary and secondary structures. Primary structures are the parts of the lattice tower structure, which dissipate the loads as a result of the wind turbine. These loads include static loads, such as those resulting from the dead weight of the wind turbine, and dynamic loads, for example, those resulting from the rotation of the rotor and from prevailing winds. Primary structures include, for example, the corner posts and the struts connecting the corner posts and extending between the corner posts. Included are also nodes, for example, cast and welded nodes. By contrast, the secondary structures have no stability-related load-dissipating function, rather they are provided to perform functional tasks and thereby distribute any occurring loads (e.g., impact loads of service ships at the boat dock) to the primary structure. Secondary structures include, for example, J tubes, platforms and docks for the landing of boats, work platforms, or pile stoppers at the anchoring end regions of the corner posts, which limit in penetration depth of a corner post when inserted into a hollow pile that is driven or drilled in the seabed. This list is only illustrative and not exhaustive. Unlike in the case of primary structures, the failure of a secondary structure does not cause deterioration of the stability of the overall construction.
In known lattice tower structures the secondary structures are connected integrally with the primary structures wherein the material of the structures is changed metallurgically such as, for example, in the case of welding. For example, platforms are welded to the corner posts or to the struts. The disadvantage of welding joints is that a notch effect is produced by the change in the metallurgical structure, through which the fatigue strength of the structure is reduced. As a result, in particular, the primary structure must be size thicker in order to compensate for the reduction in fatigue strength, which increases the cost of the lattice tower structure.
It is the object of the present invention to provide in this regard an improved lattice tower structure or openwork load-bearing structure.